Infrared sensor, nanomaterial, dispersion, and method for manufacturing infrared sensor

Abstract

The purpose of the present invention is to provide an infrared sensor capable of selecting a combination of preferable materials for an electron transport layer and a hole transport layer, and to provide a method for manufacturing the infrared sensor. This infrared sensor is provided with an electron transport layer, a light absorption layer, and a hole transport layer, and is characterized in that the light absorption layer includes quantum dots, the electron transport layer includes at least one of ZnO, MgZnO, and SnO, and the hole transport layer includes at least one of NiO and MoO. In the present invention, it is preferable that the oxygen deficiency of the metal oxide constituting the electron transport layer and the hole transport layer is smaller than that of the bulk material.

Description

Infrared sensor, nanomaterial, dispersion, and method for manufacturing infrared sensor

[0001] The present invention relates to an infrared sensor having a light absorbing layer that absorbs infrared rays.

[0002] Patent Document 1 below discloses a photoelectric conversion element having a photoelectric conversion layer that receives light in the near-infrared region and performs photoelectric conversion. The photoelectric conversion element is formed by stacking a transparent electrode, an electron transport layer, the photoelectric conversion layer, a hole transport layer, and a metal electrode in this order.

[0003] Japanese Patent Application Laid-Open No. 2021-012906

[0004] However, the invention described in Patent Document 1 does not describe anything about a preferred combination of materials for the electron transport layer and the hole transport layer in relation to the absorption edge.

[0005] The present invention has been made in view of the above points, and has an object to provide an infrared sensor that allows selection of a preferable combination of materials for the electron transport layer and the hole transport layer.

[0006] The present invention provides an infrared sensor including an electron transport layer, a light absorption layer, and a hole transport layer, wherein the light absorption layer contains quantum dots, the electron transport layer contains at least one of ZnO, MgZnO, and SnO, and the hole transport layer or the hole extraction layer contains at least one of NiO and MoO.

[0007] The present invention is characterized in that the material used in the electron transport layer of the infrared sensor described above has a slope of a Tauch plot of the absorption edge that is greater than that of the bulk material. The present invention is characterized in that the dispersion of the material described above has a polydispersity index of less than 0.1 when measured by DLS.

[0008] According to the infrared sensor of the present invention, the absorption edge can be sharply extended by the combination of materials constituting the electron transport layer and the hole transport layer.

[0009] 10A is a perspective view of an infrared imaging device equipped with an infrared sensor of the present embodiment. FIG. 10B is a partial cross-sectional view of the infrared sensor of the present embodiment. FIG. 10C is a schematic diagram of quantum dots in the present embodiment. FIG. 10D is an energy level diagram when quantum dots with a core-shell structure are used. FIG. 10E is a synthesis flow of ZnO. FIG. 10F is a synthesis flow of MgZnO. FIG. 10G is a synthesis flow of SnOx. FIG. 10H is a synthesis flow of NiO. FIG. 10H is a graph showing UV spectra, and FIG. 10I is a graph showing band gap energy. FIG. 10I is an XRD of NiO. FIG. 10I is a UV spectrum of NiO. FIG. 10I is a graph (Tauk plot) showing band gap energy of NiO. FIG. 10I is a XANES spectrum in Ni valence evaluation. FIG. 10I is a graph showing the relationship between particle size and scattering intensity distribution in Examples 1 to 3.

[0010] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist thereof.

[0011] Fig. 1 is a perspective view of an infrared imaging device equipped with an infrared sensor according to this embodiment. As shown in Fig. 1, the infrared imaging device 100 is configured to include an infrared sensor 101 and a circuit board 102. As shown in Fig. 1, the infrared sensor 101 is flip-chip bonded to the circuit board 102 via a plurality of bumps 104.

[0012] For example, the infrared sensor 101 includes a quantum dot infrared photodetector (QDIP) array in which a plurality of pixels are arranged. The bumps 104 are provided for each pixel. Note that the number of pixels is not specified in this embodiment.

[0013] The surface 101a of the infrared sensor 101 shown in FIG. 1 is a light-receiving surface. When infrared light is irradiated from the direction of the arrow, carriers confined in quantum dots within the infrared sensor 101 are excited, and the infrared light is detected as a photocurrent on the circuit board 102 side.

[0014] In this embodiment, an image sensor capable of detecting infrared rays can be realized. The infrared imaging device 100 of this embodiment can be applied to, but is not limited to, night vision devices, heat source detection devices, security devices, medical equipment, and the like.

[0015] Fig. 2 is a partial cross-sectional view showing an example of an infrared sensor (photoelectric conversion element) according to this embodiment. The infrared sensor 101 shown in Fig. 2 includes a first conductive layer 41 serving as a cathode and a second conductive layer 42 serving as an anode, and includes an electron transport layer 43, a light absorption layer 44, and a hole transport layer 45 between the first conductive layer 41 and the second conductive layer 42. For example, the first conductive layer 41 is formed on a glass substrate 46. An electron extraction layer may also be included.

[0016] In this embodiment, the electron transport layer 43 preferably contains at least one of ZnO, MgZnO, and SnO, and the hole transport layer 45 (or hole extraction layer) preferably contains at least one of NiO and MoO.

[0017] In this embodiment, the metal oxide constituting the electron transport layer 43 and the hole transport layer 45 (or the hole extraction layer) preferably has smaller oxygen deficiencies than the bulk material. In other words, a stoichiometric composition is preferable. The synthesis flow of the metal oxide according to this embodiment can suppress oxygen deficiencies. The term "bulk material" refers to a mass containing the metal oxide, regardless of size or shape.

[0018] In this embodiment, the light absorption layer 44 is a layer that absorbs light incident on the infrared sensor 101 and generates electrons and holes. The light absorption layer 44 includes quantum dots. A large number of quantum dots are dispersed and arranged within the light absorption layer 44.

[0019] The quantum dots are preferably spherical. Here, "spherical" is not limited to a perfect sphere, but refers to a sphericity of 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more. The sphericity can be measured, for example, by processing images using an electron microscope and calculating the sphericity from the area and perimeter of the observed quantum dots by 4π × (area) ÷ (perimeter). ２Alternatively, quantum dots are defined as "spherical" when the aspect ratio, expressed as the major axis / minor axis of the observed quantum dots, is 1.5 or less, preferably 1.2 or less, and more preferably 1.3 or less.

[0020] In this embodiment, quantum dots can be formed by liquid phase synthesis. The quantum dots of this embodiment are preferably spherical as described above, but are not limited thereto. Quantum dots synthesized by liquid phase synthesis may be spherical as described above, or may be formed in a shape other than spherical. Examples of shapes other than spherical include rod shapes and dendrite shapes.

[0021] For example, in this embodiment, the light absorption layer 44 can be formed using a resin composition in which a plurality of spherical quantum dots are dispersed in a resin. Here, the resin in which the quantum dots are dispersed is not particularly limited, but examples thereof include polypropylene, polyethylene, polystyrene, AS resin, ABS resin, methacrylic resin, polyvinyl chloride, polyacetal, polyamide, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polysulfone, polyethersulfone, polyphenylene sulfide, polyamideimide, polymethylpentene, liquid crystal polymer, epoxy resin, phenolic resin, urea resin, melamine resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, polyimide, polyurethane, silicone resin, cyclic polyolefin polymer (COP), cyclic polyolefin copolymer (COC), ethylene vinyl alcohol, polymethylpentene, polyvinylidene fluoride, and the like.

[0022] Alternatively, in this embodiment, a plurality of spherical quantum dots dissolved in a solvent can be applied using an inkjet method. In this case, the quantum dot layer after drying is composed of almost spherical quantum dots, but some solvent components may remain in the quantum dot layer.

[0023] Quantum dots have an emission wavelength of about 800 nm to 1600 nm. Quantum dots having such an emission wavelength include PbS, PbSe, CdHgTe, and Ag ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ It is preferable that at least one of Ag, In, and InAs is contained. ２ S does not fall under the RoHS Directive. In addition, a paper on PbS was published in 2003 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim. ADVANCED MATERIALS 2003, 15.NO.21 November 4. In addition, Ag ２ A paper on S was published in ACS NANO VOL.6 NO.5 P3695-3702 (2012).

[0024] In this embodiment, the quantum dots are PbS or Ag ２ It is preferable to use S. Also, Ag is used for the quantum dots. ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , or AgInTe ２ By using this, the fluorescence half width in the near-infrared region can be narrowed, and high-intensity near-infrared fluorescence can be exhibited.

[0025] In this embodiment, the multiple quantum dots may be of one type or two or more types. That is, the multiple quantum dots may all be of the same type, or may be of different types. The quantum dots in this embodiment are, for example, nanoparticles having a particle size of several nanometers to several tens of nanometers.

[0026] 3A, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dots 20. This makes it possible to suppress aggregation of the quantum dots 20, thereby enabling the desired optical properties to be exhibited. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples:

[0027] (1) Aliphatic primary amines Oleylamine: C １８ H ３５ NH ２ , stearyl(octadecyl)amine: C １８ H ３７ NH ２ , dodecyl(lauryl)amine: C １２ H ２５ NH ２ , decylamine: C １０ H ２１ NH ２ , octylamine: C ８ H １７ NH ２ (2) Fatty acid Oleic acid: C １７ H ３３ COOH, stearic acid: C １７ H ３５ COOH, palmitic acid: C １５ H ３１ COOH, myristic acid: C １３ H ２７ COOH, lauric acid: C １１ H ２３ COOH, decanoic acid: C ９ H １９ COOH, octanoic acid: C ７ H １５ COOH (3) Thiol-based Octadecanethiol: C １８ H ３７ SH, hexanedecanethiol: C １６ H ３３ SH, tetradecanethiol: C １４ H ２９ SH, dodecanethiol: C １２ H ２５ SH, decanethiol: C １０ H ２１ SH, octanethiol: C ８ H １７SH (4) Phosphine system Trioctylphosphine: (C ８ H １７ ) ３ P, triphenylphosphine: (C ６ H ５ ) ３ P, tributylphosphine: (C ４ H ９ ) ３ P (5) Phosphine oxide series Trioctylphosphine oxide: (C ８ H １７ ) ３ P═O, triphenylphosphine oxide: (C ６ H ５ ) ３ P═O, tributylphosphine oxide: (C ４ H ９ ) ３ P=O

[0028] In this embodiment, it is preferable to use a short ligand as the organic ligand 21. Although not limited thereto, the organic ligand 21 can be 3-mercaptopropionic acid (MPA).

[0029] The ligands of the quantum dots 20 contained in the quantum dot layer are preferably shorter than the ligands when the quantum dots 20 are formed by liquid phase synthesis.

[0030] In this way, by using short ligands for the quantum dots 20 contained in the quantum dot layer, the roughness of the quantum dot layer can be reduced and the electron and hole extraction efficiency can be improved. On the other hand, by using long ligands when forming the quantum dots 20 by liquid phase synthesis, the dispersion and film formation properties can be improved.

[0031] Alternatively, quantum dots 20 with long ligands may be synthesized by a liquid phase synthesis method, and then the composition containing the quantum dots 20 may be replaced with a short ligand (e.g., 3-mercaptopropionic acid) before or after application.

[0032] 3B, the quantum dot 20 may have a core-shell structure having a core 20a and a shell 20b covering the surface of the core 20a. As shown in FIG. 3B, it is preferable that a large number of organic ligands 21 are coordinated to the surface of the quantum dot 20. The organic ligands 21 are as described above. The core 20a of the quantum dot 20 shown in FIG. 3B is the nanoparticle shown in FIG. 3A. Therefore, the core 20a is formed, for example, from the material of the quantum dot 20 listed above.

[0033] The shell 20b may be in a state of being solid-solutioned on the surface of the core 20a. In Fig. 3B, the boundary between the core 20a and the shell 20b is shown by a dotted line, but this means that the boundary between the core 20a and the shell 20b may or may not be confirmed by analysis. Although not shown, it is preferable to have a buffer layer between the core 20a and the shell 20b. The buffer layer is a region in which at least some or all of the elements constituting the core 20a and at least some or all of the elements constituting the shell 20b are mixed.

[0034] In this embodiment, the structure is one in which spherical quantum dots are applied, and quantum dots (particularly spherical quantum dots) formed by, for example, a liquid phase synthesis method are used, so that the sensitivity is excellent in all directions, and the variation in sensitivity can be reduced compared to, for example, microfabricated quantum dots.

[0035] In this embodiment, the quantum dots are PbS, PbSe, CdHgTe, Ag ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ It is preferable that the material contains at least one of InAs and InAs. These have an emission wavelength of 800 nm to 1600 nm and can be suitably used in infrared sensors.

[0036] When the quantum dots applied to this embodiment have a core-shell structure, the energy level diagram will be any one of those shown in Figures 4A to 4D. In the case of a light-emitting device, the shell of the core-shell structure is important in terms of improving the quantum confinement effect. The type I structure shown in Figure 4A (where the LUMO of the shell has a higher energy than the LUMO of the core, and the HOMO of the shell has a lower energy than the HOMO of the core) is particularly preferred.

[0037] On the other hand, when used in a photoelectric conversion element as in this embodiment, a type II structure is preferred so that carriers (electrons, holes) can be easily extracted. However, since hole mobility is usually lower than electron mobility, it is preferable to select type II(1) or (3). When used in a photoelectric conversion element, quantum dots having a core structure with a ligand can also be used instead of a core-shell structure. In type II(1), the LUMO of the shell has lower energy than the LUMO of the core, and the HOMO of the shell has higher energy than the HOMO of the core. In type II(3), the LUMO of the shell has higher energy than the LUMO of the core, and the HOMO of the shell has higher energy than the HOMO of the core. In this embodiment, the film thickness of the light absorption layer is preferably 5 nm or more and 50 nm or less.

[0038] (Electron Transport Layer 43) The electron transport layer 43 is made of an inorganic or organic material having a function of transporting electrons. In this embodiment, the electron transport layer 43 contains at least one of ZnO, MgZnO, and SnO. Two or more of these may be selected. The electron transport layer 43 is particularly made of ZnO. Ｘ It is preferable that the metal oxide is formed of nanoparticles of the metal oxide. The metal oxide may be doped with Li, Mg, Al, Mn, etc. X is not limited to, but is about 0.8 to 1.2, and it is preferable that there is no oxygen deficiency.

[0039] The electron transport layer 43, like the light absorption layer 44, can be formed by printing a solvent containing nanoparticles using a printing method such as an inkjet method, or by using an existing thin film technology such as a vacuum deposition method.

[0040] (Hole (Positive Hole) Transport Layer 45 or Hole Extraction Layer) The hole transport layer 45 is made of an inorganic or organic material having a function of transporting holes. In this embodiment, the hole transport layer 45 or the hole extraction layer preferably contains at least one of NiO and MoO. The hole transport layer 45 or the hole extraction layer may contain, for example, NiO with Al. ２ O ３ It is also possible to mix the metal oxide with Li, Mg, Al, etc. The metal oxide constituting the hole transport layer 45 or the hole extraction layer preferably does not have oxygen deficiency.

[0041] The method for manufacturing an infrared sensor according to the present embodiment includes a step of forming spherical quantum dots by liquid phase synthesis, and a step of forming a light absorbing layer by applying a resin composition containing the quantum dots.

[0042] In this embodiment, the liquid phase synthesis method involves dissolving the respective element sources constituting the quantum dots in a solvent, and reacting the precursor solutions containing the respective elements using, for example, a microreactor, to synthesize quantum dot particles containing the desired elements, thereby obtaining spherical quantum dots.

[0043] To improve the dispersibility of quantum dots, it is preferable to use long-chain ligands. Therefore, quantum dots having long-chain ligands are preferable for application, but for device fabrication, short-chain ligands are preferable to increase the efficiency of carrier (electron, hole) extraction. Although not limited thereto, the number of carbon atoms in the short-chain ligand is 2 to 5 (preferably 2 to 3). For example, 3-mercaptopropionic acid can be used as the short-chain ligand.

[0044] In this embodiment, quantum dots can be synthesized by liquid-phase synthesis, and then the quantum dot ligands can be replaced with short ligands. For example, a quantum dot-containing composition (including quantum dots and a solvent) is applied using a spin coater. Long-chain ligands have better dispersibility and can form films with good roughness. However, long-chain ligands are disadvantageous for carrier extraction. Therefore, for example, after application, short-chain ligands are dripped onto the coating film. This naturally replaces the long-chain ligands with short-chain ligands, and the coating is then washed away. Alternatively, quantum dots can be synthesized by liquid-phase synthesis, and then the long-chain ligands can be replaced with short-chain ligands before application, and then a quantum dot-containing composition (which may be a resin composition) can be applied. In this embodiment, the electron transport layer 43 is formed from ZnO, MgZnO, or SnO. The synthesis flow for these metal oxides is described below.

[0045] Figure 5 shows the synthesis flow of ZnO. As shown in Figure 5, Zn(OAc) ２ ・2H ２ O (6.22 g, 28.3 mmmol) and 0.5 wt% hydrous methanol (198.8 g, 251 ml) were mixed and the temperature was raised to 60°C. Next, KOH / 0.5 wt% hydrous methanol was added to the flask at a rate of 13 ml per minute, and this addition was continued for 10 minutes. The temperature was then maintained at 60°C for 2 hours.

[0046] After cooling, the mixture was transferred to two centrifuge tubes and centrifuged at 7000 pm for 5 minutes. The supernatant was then removed from each tube, and the mixture was sonicated and centrifuged again at 7000 pm for 5 minutes. The process of removing the supernatant, sonicating, and centrifugation was repeated once more.

[0047] Then, the supernatant was removed and ultrasonication was performed, and between the removal of the supernatant and the ultrasonication, ethanol (5 ml) and aminoethanol (0.5 ml) were added to each centrifuge tube, and the tubes were then stored overnight in a dark place.

[0048] Next, the mixture was transferred to two other centrifuge tubes, and about 35 to 40 ml of ethyl acetate was added to each tube, followed by centrifugation at 5500 rpm for 5 minutes. The supernatant was then discarded from each tube, and the mixture was transferred to a G-BOX and dispersed using a vortex mixer.

[0049] Next, the solution was passed through a 0.54 μm filter and transferred to a 50 ml tube, from which 0.7 ml was taken, and the remainder was stored in a G-BOX. The concentration of the taken 0.7 ml was measured, and the concentration and dilution ratio were calculated. Based on this calculation, the dilution ratio was adjusted to the calculated value using dehydrated ethanol in the G-BOX. The completed G-BOX was then stored. A 1.6 ml aliquot was taken from this completed G-BOX, and DLS, UV value, PL value, and concentration were analyzed.

[0050] 6 shows the synthesis flow of MgZnO. As shown in FIG. 6, first, anhydrous ethanol (30 mL) was prepared, and Zn(OAc) ２ ・2H ２ O (560 mg, 2.55 mmol) and Mg (OAc) ２ ・4H ２ O (96.5 mg, 0.45 mmol) was added and stirred at room temperature for 30 minutes. Subsequently, KOH (309 mg, 5.5 mmol) / absolute ethanol (20 mL) was added. Then, stirring was continued at room temperature for 1 hour. Subsequently, hexane (80 mL) was added. This resulted in the mixture becoming cloudy white. Ethanolamine (1 mL) was added to this mixture until it dissolved, and further hexane was added to precipitate the solid, which was then dispersed in ethanol. This resulted in the production of MgZnO with a particle size of approximately 4.2 nm. The band gap energy E of MgZnO was ｇ was 3.79 eV.

[0051] Figure 7 shows the synthesis flow of SnOx. As shown in Figure 7, ethylene glycol (100 mL) was prepared, and SnCl ４ ・5H ２O (11.57 g, 0.33 mol), acetic acid (10 mL), and 30% aqueous tetramethylammonium hydroxide solution (25 mL) were mixed and stirred at 50°C for 30 minutes. The temperature was then raised to 160°C and stirring was continued for 4 hours. The mixture was then washed with ethanol-ethyl acetate, and 2 mL of ethanolamine was added, followed by dispersion in ethanol.

[0052] In this embodiment, the hole transport layer 45 or the hole extraction layer is formed of NiO or MoO. The synthesis flow of these metal oxides will be described below.

[0053] Fig. 8 shows the synthesis flow of NiOx. As shown in Fig. 8, DMSO (100 mL) was prepared and Ni(NO ３ ) ２ ・6H ２ O (10 mmol) and KOH (673 mg, 12 mmol) in absolute ethanol (100 mL) were mixed and stirred at room temperature for 30 minutes. Subsequently, after washing with ethanol, DMSO (150 mL) was mixed and stirred at a temperature of 160°C for 4 hours. Next, it was washed with ethanol-ethyl acetate, and ethanolamine (0.2 mL) was added and dispersed in ethanol. A dark gray precipitate was obtained.

[0054] 9 shows the synthesis flow of MoOx. 1-octadecene and octanoic acid (total volume 60 mL, volume ratio of 1-octadecene:octanoic acid = 1:9) and MoOx were placed in a sealed tube. ２ (acac) ２ (244.62 mg, 0.75 mmol) and acetic acid (10 mL) were mixed and stirred at 50°C for 30 minutes. The temperature was then raised to 180°C and stirred for 40 minutes, and n-octane (250 mL) was added to obtain a dark blue precipitate. The precipitate was dispersed in ethanol.

[0055] According to the synthesis flow of this embodiment, a metal oxide free from oxidation defects can be obtained. Furthermore, by using the electron transport layer and hole transport layer of this embodiment, it is possible to effectively and sharply extend the absorption edge in the infrared region.

[0056] FIG. 10A is a graph showing the UV spectrum, and FIG. 10B is a graph (Tauk plot) showing the band gap energy. In the experiment, the amount of Mg doping in MgZnO was changed. Note that the MgZnO used in the experiment was immediately after synthesis and dispersed in DEGME. As shown in FIG. 10, as the amount of Mg doping increased, the band gap energy E ｇ was found to increase.

[0057]

[0058] FIG. 11 shows a synthesis flow of NiO. Note that this synthesis flow is different from that shown in FIG. 8. That is, as shown in FIG. 11, ３ ) ２ ・6H ２ O, dimethyl sulfoxide, and KOH / absolute ethanol solution were mixed and stirred at room temperature for 30 minutes. This resulted in a green precipitate. This was mixed with DMSO, kept at 160°C for 3 hours, and washed with ethanol / ethyl acetate. Ethanolamine was then added and dispersed in ethanol.

[0059] Figure 12 shows the XRD of NiO. The NiO used in the experiment was obtained using the synthesis flow shown in Figure 11. As shown in Figure 12, NiO was observed. However, Ni was not observed, indicating that the NiO was properly synthesized. Figure 13 shows the UV spectrum of NiO, and Figure 14 is a graph (Tauk plot) showing the band gap energy.

[0060] As shown in FIG. 14, the slope of the Tauch plot of the absorption edge was found to be greater than that of the bulk material. This indicated that the absorption edge could be sharply extended. Furthermore, as shown in FIG. 14, the Tauch plot for nanoparticles showed a steeper rise with a smaller tail than that for bulk material. Because all of the electron transport materials in this example were semiconductors, the slope of the Tauch plot for all electron transport materials was greater than that for bulk material. Furthermore, as shown in FIG. 14, the regions A and B enclosed by the tangent line indicating the slope, the plot curve, and the horizontal axis were found to be smaller for nanoparticle region A than for bulk material region B. Since the oxygen vacancies become smaller as this region becomes smaller, it was proven that nanoparticles have smaller oxygen vacancies than bulk material.

[0061] <Regarding Ni valence of NiO> Standard samples with known valence (NiO: divalent, LiNiO ２ A calibration curve of the rise position of the XANES spectrum and the Ni valence was created using the BL08W beamline and the transmission method for the measurement.

[0062] Next, the Ni valence was evaluated from the XANES spectrum of NiO prepared by the synthesis method of this example. The experimental results are shown in FIG.

[0063] As shown in Figure 15, it was found that the XANES spectrum shifted due to the change in valence. ２ Since the XANES spectrum of the example exists between the trivalent and trivalent states, the Ni valence of the NiO of the example is between 2 and 3, leaning toward divalent NiO. Therefore, it was found that the Ni valence of the example is greater than 2 and less than 2.5, preferably 2.1 or more and 2.4 or less. In the example of Figure 15, the Ni valence is predicted to be about 2.2. This proves that the NiO of the example is a hole carrier.

[0064] Furthermore, the polydispersity index of the metal oxide dispersion used in the electron transport layer of this example was less than 0.1 when measured by DLS. Dynamic light scattering (DLS) is applied to nanoparticles suspended and dispersed in a liquid. DLS measurement is a method for calculating particle diameter by measuring the diffusion rate of nanoparticles moving by Brownian motion.

[0065] The polydispersity index (PDI) is used to represent the width of the particle size distribution. In the experiments, ZnO particles were prepared as the metal oxide used in the electron transport layer. Figure 16 is a graph showing the relationship between particle size and scattering intensity distribution in each example. As shown in Table 2, the polydispersity index was less than 0.1 in each of Examples 1 to 3. This shows that all of the particles measured in each example had approximately the same particle size.

[0066]

[0067] Metal oxides such as ZnO and NiO exist as a film in an infrared sensor. In this embodiment, the polydispersity index is set to less than 0.1 as described above to improve dispersibility, but the performance of the film can be defined as the surface roughness after film formation.

[0068] That is, the surface roughness Ra (arithmetic mean roughness) of the film is preferably less than 1.0 nm. The surface roughness (Ra) can be analyzed by AFM measurement or the like.

[0069] According to the present invention, infrared detection is possible. The infrared sensor of the present invention can be applied to night vision devices, heat source detection devices, security devices, medical equipment, etc.

[0070] This application is based on Japanese Patent Application No. 2023-170555, filed September 29, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. An infrared sensor comprising an electron transport layer, a light absorption layer, and a hole transport layer, wherein the light absorption layer contains quantum dots, the electron transport layer contains at least one of ZnO, MgZnO, or SnO, and the hole transport layer or the hole extraction layer contains at least one of NiO or MoO.

2. The infrared sensor according to claim 1, wherein the oxygen deficiency of the metal oxide constituting the electron transport layer and the hole transport layer is smaller than that of the bulk material.

3. The infrared sensor of claim 1, wherein the quantum dots include an organic ligand on the surface, the organic ligand including 3-mercaptopropionic acid.

4. The infrared sensor according to claim 1, wherein the quantum dot includes a ligand on the surface, the ligand having 2 or more and 5 or less carbon atoms.

5. A nanoparticle material used in the electron transport layer constituting the infrared sensor according to claim 1, characterized in that the slope of the Tauch plot of the absorption edge is greater than that of the bulk material.

6. A dispersion of the material of claim 5, characterized in that the polydispersity index, as measured by DLS, is less than 0.

1.

7. A method for manufacturing an infrared sensor according to claim 1, characterized in that in the step of forming the light absorbing layer, after applying the composition containing the quantum dots, a ligand is exchanged.

8. The method for manufacturing a display device according to claim 7, characterized in that, when the quantum dots are synthesized by a liquid phase synthesis method, the quantum dots are synthesized using long ligands, and then the ligands are replaced with short ligands before or after applying a composition containing the quantum dots.

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